Wikipedia:Reference desk/Archives/Science/2016 July 28

= July 28 =

Hearing Distance in humans.
Where would I find out, how far away a 'wanted' sound can be heard by a normal human?

(Context is that when reading about Dutch cycling rules I came across some requirement that cycle bells apparently had to be heard 25m away. I'm assuming that this would be for normal hearing under typical conditions.)

I imagine that determining how far away a specific sound can be heard is more complex than first seems. Sfan00 IMG (talk) 13:03, 28 July 2016 (UTC)


 * "In a normal three-dimensional setting, with a point source and point receptor, the intensity of sound waves will be attenuated according to the inverse square of the distance from the source." Measure the decibel level of the bell and using the above law calculate the distance where the decibel level is not discernible to humans. 196.213.35.146 (talk) 13:37, 28 July 2016 (UTC)
 * Yes, but the inverse square law just implies that the attenuation obeys the format I = k * (1/d2) where I is intensity and d is the distance from the source. The problem is that k, the constant, is itself a complex function, and will be dependent on both the wavelength of the specific sound (lower frequency sounds travel farther, see for example infrasound) and the medium itself (i.e. the air properties such as density, temperature, pressure, and humidity, all of which change a lot).  While bringing up the inverse square law makes it sound simple, the devil is in the details, and the details (the "k" factor here) are quite devilish. -- Jayron 32 18:26, 28 July 2016 (UTC)
 * It is indeed quite complex. This may help Decibel. 196.213.35.146 (talk) 13:41, 28 July 2016 (UTC)


 * The Phon might interest you. 196.213.35.146 (talk) 13:44, 28 July 2016 (UTC)


 * Silbo_Gomero says (with reference) that that whistled language can be used to send an auditory message 5k in good conditions. SemanticMantis (talk) 13:52, 28 July 2016 (UTC)
 * 5k? Do you mean 5 KM? ←Baseball Bugs What's up, Doc? carrots→ 17:30, 28 July 2016 (UTC)
 * Clicking on my link would have clarified that I meant five kilometers. The more appropriate symbols would have been '5 km'. From our kilometre article: "k (pronounced /keɪ/) is occasionally used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech." For example, I often hear runners saying "I ran five kay yesterday". SemanticMantis (talk) 18:34, 28 July 2016 (UTC)
 * Either KM or km work. In the recent Tour de France broadcast, they showed the remaining distance alternating between miles (MI) and kilometers (KM). ←Baseball Bugs What's up, Doc? carrots→ 22:04, 28 July 2016 (UTC)


 * After digging around a bit for "peak frequencies", I came across this article, Psychoacoustics, which is rather interesting. DrChrissy (talk) 19:07, 28 July 2016 (UTC)


 * John Tyndall, in "The Science of Sound", devotes chapter 7 to things that affect the propagation of sound through the atmosphere. The motivation seems to have been fog horns and shipping safety.  This was in 1875, and understanding has probably advanced some since then.--Wikimedes (talk) 21:01, 28 July 2016 (UTC)


 * On the subject of foghorns. They were noticeably audible because of the long duration. They made the air vacillate. Bit like what the Alphorn does, and on which one doesn't try to play the Trumpet voluntary as the sound just would not carry so well. So perceivably (subjectively)  they were more perceptible . The Buncefield fire explosion in Hemel Hempstead was heard as far a way as Holland but that was probably due to an early morning atmospheric condition  (an inversion) which tunnels the sound. It woke me up and I live miles and miles away.  So I don't see how we can really answer the OP's question because if one sets up a long duration sign wave sound source it can travel for miles and mile  depending on the atmospheric conditions.--Aspro (talk) 22:08, 28 July 2016 (UTC)
 * Somewhat related, a former prof of mine has extensively studied the propagation of elephant calls under different atmospheric conditions. Although it's about elephants some of the basic ideas are general. Interesting stuff; an article on it is here. Shock Brigade Harvester Boris (talk) 03:22, 29 July 2016 (UTC)
 * I'm surprised that article did not mention seismic communication in elephants. In some circumstances, they are believed to actually hear through their feet! DrChrissy (talk) 21:27, 30 July 2016 (UTC)


 * I refrained from mentioning that, as the OP's question was about human hearing. But I'm surprised why you DrChrissy did not  also mention  that elephants can also communicate long distances, by apparently just picking up the telephone and making trunk calls?  --Aspro (talk) 12:58, 31 July 2016 (UTC)


 * Humans can also "hear" through their feet. IIRC, Heather Whitestone listened with her feet for the music when she danced in the Miss America competition. Collect (talk) 23:00, 30 July 2016 (UTC)
 * Atmospheric conditions can do funny things with sound. The 1980 eruption of Mount St. Helens was audible in some far away places but not audible in some closer places. ←Baseball Bugs What's up, Doc? carrots→ 03:41, 29 July 2016 (UTC)


 * EO dates the term "tinny" to 1877, which is shortly after the invention of the telephone. ←Baseball Bugs What's up, Doc? carrots→ 17:34, 29 July 2016 (UTC)

Identifing sound from batbox
I put this batbox up only a few months ago so I'm surprised to already be hearing activity inside as instructions state it may take years for bats to settle. So I'm not sure if what's inside is a bat - I haven't seen anything leave or enter. I recorded the sound made. https://vid(dot)me/xeHw

Any luck in identifying species? edit: I live in the West Midlands in the UK79.68.175.188 (talk) 17:38, 28 July 2016 (UTC)


 * When I click on the link I get "Server not found". Bus stop (talk) 17:45, 28 July 2016 (UTC)


 * replace the (dot) with a . 79.68.175.188 (talk) 17:46, 28 July 2016 (UTC)


 * OK, thanks. Bus stop (talk) 17:49, 28 July 2016 (UTC)


 * Sounds like a bat to me. Compare e.g. this recording It's not exactly the same, but similar, search youtube for more examples. I'm not sure what specific type of box you used by most bat boxes are designed to be not attractive to e.g. birds, non-flying rodents, and other things that might like a box. It MAY take years, but I think you got lucky and had bats move in more quickly. Keep an eye out near dusk and hope to catch them leaving :D SemanticMantis (talk) 18:29, 28 July 2016 (UTC)


 * I have often wondered if the microphones built into smart phones have a high enough frequency response to pick up bats. If so, they would only need an app with a software 'heterodyne' to make the ultra sounds audible. Any kick-starters out there (?) as a dedicated bat  heterodyne detector can cost over a £100. With one of those one can identify one's bat. Bat Detectors. Mind you, if the critter is weareing a a yellow cape, a green mask, a red jerking  and tights, it is probably a Robin.--Aspro (talk) 21:23, 28 July 2016 (UTC)
 * "Holy mis-identification Asproman!" Another piece of technology you could use is a camera trap, sometimes called trail cameras. DrChrissy (talk) 21:33, 28 July 2016 (UTC)
 * Lol. Images would indeed help for ID, and so would ultrasonic information. For clarity, many bat vocalizations are outside normal human hearing range, but they do plenty of chattering vocalization in the human hearing range too. Also WHAAO trail cameras and camera traps (which are different articles that perhaps should be merged, if anyone is feeling bold). SemanticMantis (talk) 21:45, 28 July 2016 (UTC)


 * It would (in a perfect world) be advantageous to place a web cam in the box from the out set. One can't (as you will already know) do it after they start roosting, unless one has a license permitting one to handle bats and make adjustments to their habitat. Trail cameras however, are a bit tooo slow for the amateur -me thinks. They have an in built delay which needs some knowhow to adjust. This is because if they fired immediately, all one will see is the snout of a badger or something. So a (typically) ten second delay is built in with the hope that the whole critter is in view buy the time the exposure is taken. I haven't came across one suitable for bats yet. I can't even see bats on my night scope (admittedly it is a cheap one and not a class III military spec). The image is clear but the response is too slow to for the fast moving bats to register. Maybe better to use use a infra red video camera at  dusk whilst there is still some light. And anyway, if one could get a image on a  Trail cam it would be so blurred that even an expert would not be able-to identify it. Lots of bats look the same. Finally, It would be interesting to know the circumstances of how the OP came by the bat box to start with. He is right that they don't usually get inhabited so quickly. The reason  - I think-  is that freshly cut wood releases terpenoids  and esters, which  to a bat, in confide confined space,  must be pretty suffocating until the wood has seasoned (about two years minimum). So did the OP by chance get his hands on a old matured box?--Aspro (talk) 23:06, 28 July 2016 (UTC)


 * Perhaps you could try contacting you local bat group for assistance? https://batlasproject.wordpress.com Their site contains the species found in the West Midlands. --TrogWoolley (talk) 08:59, 29 July 2016 (UTC)


 * That's a good point about the age of the wood, but the wood pictured in the video does not look young to me. SemanticMantis (talk) 14:41, 29 July 2016 (UTC)

Would the existence gravitational waves imply the possibility of antigravitational waves?
All sources I find about the latter gravitate around sci-fi or cracks who developed anti-gravity-like devices. Hasn't the possibility being seriously considered? Hofhof (talk) 21:58, 28 July 2016 (UTC)


 * Depends, what do you mean by "antigravitational waves"? As it passes, every gravitational wave will stretch some of space and compresses other parts of space, depending on its orientation.  One can also imagine a new gravitational wave that compresses the things the first wave stretched (and vice versa), but that is just a differently polarized gravitational wave.  So a gravitational wave with the opposite effects of the first wave is just a different kind of gravitational wave.  Is that what you mean, or were you imagining something else by "antigravitational"?  Dragons flight (talk) 22:17, 28 July 2016 (UTC)


 * One thing I was thinking on was what you describe. The other would simply be matter that repels matter, unless of attracting it. --Hofhof (talk) 22:24, 28 July 2016 (UTC)


 * Matter that gravitationaly repels other matter is not theoretically prohibited by either general relativity or quantum mechanics, but there is no known form of matter with this property. The existence of gravitational waves doesn't change that, since their existence was derived from GR to begin with. The article you're looking for is negative mass. Someguy1221 (talk) 22:37, 28 July 2016 (UTC)


 * I think that gravitationally repulsive matter is forbidden by field theory (even classically) because it's a perturbation of the vacuum with lower energy than the vacuum itself, and that means the vacuum is unstable. In general relativity, you get weird pathologies (notably closed timelike curves) if you permit locally negative energy density. Probably the deeper theory of gravity that general relativity approximates is fundamentally inconsistent with negative energy. -- BenRG (talk) 06:09, 30 July 2016 (UTC)


 * Existence of gravitational waves, if confirmed, would raise questions like 1) what is their supporting medium such as an "aether", or have they none other than a mathematical consistency of simultaneous differential equations such as Maxwell's for electromagnetic waves; 2) do they have all the degrees of freedom that we expect in waves (amplitude, frequency, phase); and 3) are there non-linear effects (comparable to dispersion in optics or to diodes, transistors and logic gates in electronics) that we might exploit? A rich source of speculation is that sound waves have already demonstrated ability to manipulate small objects - see Acoustic tweezers - including levitating a few kilograms. However by the rules against speculation on this desk, we should confine the references we give to the First observation of gravitational waves. AllBestFaith (talk) 10:45, 29 July 2016 (UTC)


 * The existence you propose would allow for regionally suppressing gravity, but not "negative" gravity - repelling things. Just like noise-cancelling headphones car eliminate noise but not create negative noise. -- Q Chris (talk) 11:50, 29 July 2016 (UTC)
 * "Negative Noise" would be a pretty cool band name. Shock Brigade Harvester Boris (talk) 03:49, 1 August 2016 (UTC)


 * Has anyone ever seen anti-sound waves or anti-waves on the sea or anti-light waves or have any idea what any of them would be supposed to be? I guess I could have done with something emitting anti-heat waves recently like Arnold Schwarzenegger as Mr Freeze in a Batman movie ;-) Dmcq (talk) 12:29, 29 July 2016 (UTC)


 * This not only would be theoretically interesting but would result in a useful commercial product. Something like a "reverse microwave" to cool things quickly. Shock Brigade Harvester Boris (talk) 12:35, 29 July 2016 (UTC)


 * First, isn't the hypothetical graviton its own anti-particle? Second, I am not aware of anti-electromagnetic waves.  While every particle is thought to have an anti-particle unless it is its own anti-particle, not every wave has an anti-wave.  Third, negative gravity would require, not negative gravity waves, but negative mass, and I think that does pose technical challenges.  Robert McClenon (talk) 12:48, 29 July 2016 (UTC)